Speedometer temperature compensator



March 1, 1932. l. T. WEDIN SPEEDOMETER TEMPERATURE COMPENSATOR Filed Feb. 6, 1929 2 Sheets-Sheet March 1, 1932. f wEDlN 1,848,068

' SPEEDOMETER TEMPERATURE COMPENSATOR Filed Feb. 6, 1929 =2 Sheets-Shes; 2

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Patented Mar. 1, 1932- UNITED ST E IVAR T. WEDIN, on

FLINT, MICHIGAN, AssIGNoit T Ao SPARK PLUG 'coMrAiiY; or .J rum, MICHIGAN, A COMPANY OFMICHIGANY SPEEDOMETERQEMBERATURE oomrmrsaronf 3 1 Application filed February a, 1929. Serial KO. 337,929.

This invention relates to measuring instruments and has been designed more particular ly as an improvement inthe temperature com pensating' provision for 'magnetic 1 speedom- ,;,-5 etersf such as are used on motorvehicles. i

An object of the invention is toprovide a compensator having maximum efiicie'ncy in rendering the reading of the instrumentiac curate withina wide range' of temperature changes. 1' a "Another'object is to accomplish-the above mentioned phject with a structural arrangein'ent which. s simple, inexpensive "and easily applied.

- other zi a dvantages W111 a ap- 7 n ly illustrated.

parent fromthe following description. In the drawings: is

"Figure 1 is 'a' vertlcalfse'ctionthrough" a magnetic speedometer my lmproved jtem perat'ure compensator being 1ncorporated therein," a v g Figure 2 is a transverse sectlon sub'stan; tia'lly on line 2+2ofF1gure o1.

" Figure'3-is a top planview of a modifica- I 2 tion parts broken' away andin sectionto vice. I Y

Figure at is a vertical section substantially on line 4- 4of F1gure 3.

illustrate the use of the compensating de-.

1 Figure 5; is a section corresponding to Fig ure 1, this 'figure showing a modified form of the compensator. 1

Figure 6 is a view taken. from line 6 -6 of ."Figure '5.

y Figure 5. a I v p U I Figure 8 is a section on line 8 8f fFi' ure 6. V v. a

corresponding ure3. p Figure 10 is asectionon'line .1 0-g1'0' of Figure'9.

=use d in Figure 9, and

V Figure 12 isj 90ti n o'n' line 12 ,f

Figure 11. I

Figure/.7 is avrprspective of the: p theponicalnfieldqplatei The extremet-endof $5 I sator 'used'in the form of .thein'venti'on shown Figure 11 isaplan view ofithe compensator I s V .the other" inthe apex of-the conical-field 5 is housed within a casing 7 The frame is to carry the speedometerp'arts'jand the ca s? ing is seated against a flange 9 of theframe to which it" may be secured in any" conven- -tional way, not shown. The frame" has a $5 stem'part llexterna'lly threaded as atE13 for attachment toga niit associated with the con} i -pling'meansforthe'fiexibledrive shaft. The,

fram'efis also internally bored to receive a worm shaft 15,]the latterangularly'relatedlto the front face of the instrumentf; At its out er end wori'n shaft 15, 'isiformed with openings'to receive the usual connecting means associ ated with the fiexible drive shaft. These features 'are not apart ofthis'invention '-65 worm shaft 15 i sfgeared' to ase'cond wofni s'haft '17 5 this beingthe streamed second worm shaft of the speedometer; At one end shaft'-17"has.' an "eccentric 19 serving to reliprocafie r o edby sP1-ii g 23 the pawl operating through a suitablemeans to rotate the "figure wheels'of an o dometer. gne of the o'domete r"wheels being-designated 1f; The frame atfits top portio n'has: diverging V arms','one,of which is shownat27. To these arms are} connected' lug's extending from a conical field plat'e29; i i

The end of shaft 1,5;is reduced, the

.'rid p si g t l l l am nene hiearma- :net 31, the en dsof which are upturned to lie in parallel lrelation'with the adj oining of shaft: :15 vis riv'eted-Over-to hold the -imagn et' in position, as will be obvious: V -"similarly:- sha'pe'd conical speed-5011p or indicating member 33 is located' -hetw'een the field'plateand'the magnet, its conical..wal'l "being parallel with theconical wall of: the

field plate; a This speed cup ismounted on: a spindle "35' journalled in bearings carried by Ljewel cups 37 andy39'positioned in-alignment andlocate'dlone'inithe end-'ofshaft 15 -an'd .spindle'35 atone end and' toa' regulator 43 rotatably mounted about the upper bearing the extreme end of spindle 35 to limit the axial movement of the same.

Means such as struck up flanges l5 and 47 on the field plate and speed cup limit the rotation of the latter under the influence of the hair spring. The field plate is open at its front to render visible the indicating characters on the speed cup and is provided with a point-er 49 to aid in reading the instrument. e

A cover plate 51, a glass 53' anda bezel"55 are used at the front of the instrument, these parts being conventional and'not'constituting a part of this invention.

The construction described is very efficient This isparticul'arlytrue in the case of the conical Walled. speedcup and gfield plate With the magnet ends positioned in. parallelism with said walls. 3 a y As is-wellknoivu, the electricalresistance of the non-magnetic speed cup increases as thetemperature rises With-the result that the readings of. the instrument tend. to be too low at temperatures above that atwhich the instrumentis calibratedmndtoo high at lower. temperatures. One known Way :ofcorrecting for this error. is to. provide a shunt includinga part, preferably air-alloy, the magnetic permeability of which decreases as the temperature rises. i

In. connection with. an instrument as describedI =use athermo-compensating unit 57 formed of a thermo-compensating alloy which is-shaped like the magnet and attached theretoeby pinching the metal to distort it in places to-form clamping. ears 59.

A compensator of thiskindis-found to be highly ellicient. In previous expedients employing an alloy compensator, the compensator hasbeen used as or as a part of an external shunt which is tobe distinguished from the'active magnetic field; the fi eld active upon the speed cup. In" the present case the equivalent of the shunt is Within the-magnet itself. v V a. AS is well known. at temperatures lower than those for which theinstrument is caliin g shunted through t-hecompensator than at the calibration temperature.

On the other: hand when. the temperature rises above that. for which theinstrument iscal'ibrated and owing to thegr-eater electrical resistance of the speed cup at the higher temperature as a result of which readings would tend to be too low, the lesser magnetic permeability of the compensator causes less of the magnetic flux to be shunted from the pole through the compensator and more to pass through the speed cup. There isfltherefore a compensation provided for in which the lines of force are at all times under con- =trol-. the proportion passing through the shunt so controlling the proportion through the active fieldas to insure correct readings at all temperatiiires.

Wehave therefore a temperature compensator unit which is attached to and made a part of the rotating magnet, rotating axially thereof and positionedwithin the magnetic field and functioning thereW-ithin. It con .trols Withi-nathe magnetic field the intensity of magnetic current before passing through the speed cup. Walls and previous to its infiuenceuponthespeed cup. It givesmaximum accuracy of; speed indication at all tempera tures within areasonable range.

Since. also the full strength of the magnet is being used Withinthe speed cup a. more definite control. is had than Witlrother. arrangements, both the active field and the shunt being shielded. It is possible to quite accurately determine the electrical resisting characteristics of the speed cup metalunder temperature changes and to so determine the dimensions of the compensator as to secure very accurate readingat all temperatures.

Figures 3 and 4 show another type of -in strument in which the invention maybe em bodied. In this second .form there is-a fixed U-shaped magnet Within which is a rotor 71. The magnet is held in position by a clamp/('3. Rotor 71 is driven by shaft 75'. Speed cup 77 is carried by a spindle TQWl'IlCh is suitably journalled so that the cup rotates between the poles in such a Way that by far the greater part of thelines of force are cut by the rotor as it rotates. At 79 is a compensatorunit. This unit has the same characteristics as compensator 57 of the-form described above. v

In this second embodiment of the invention'the compensator is Within the rotor; and

having magnetic permeability characteris tics'the opposite of the electrical resistance of the-speed. cup aids in maintainingin. the active field across the gap such a flux as-to produce accurate readings at all temperatures.v \Vhile the strength of the field is not decreased or increased before acting :upon the speed cup as in the form described above,

the intensity of the magnetic current effective through the cup is directly controlled and made uniform.

' In this second form of the invention the intensity of the magnetic current generated by the rotor is directly controlled by th'e'compensator which will increase or decrease the strength of the magnetic current passing through the speed cup according to its permeability to proportionately compensate for the relatively high or low resistance ofthe speedv cup during temperature changes.

Figure shows a form of, the invention similar to that of Figure 1 but with a somewhat different form of compensator.

In this figare the reference characters are the same as for the corresponding parts in Figure 1. The compensator comprises a stamping shown in perspective in Figure 7 and designated by reference character 101. It has slotted wings 103 diverging from the apertured base 105. Projections 107 are to be bent over the magnet and serve to hold the compensator in position.

poles. This form of compensator'is easily made and as easily assembled. It willadjust itself automatically to form positive contact points with the poles irrespective of any 1 warpagewhich may occur. 'Owingto itsshape as compared with the shape'of the compen' The leg portions of the slotted wings 103 are in contact with the magnet within said magnet, said compensator being secured to said base portion of said magnet and having slotted wings contacting with the corners at said ends of said magnet.

In testimony whereof I aflix my signature. IVAR T. WEDIN.

sator shown in Figure 1 it tends tojshorten its shunt action across from pole to pole.-

The action is substantially the same as the compensator shown in Figure 1 but is be lieved, for the reasons stated, to be apreferable form. c p

Figures 9-12 show a modified form of the compensator used in the relation shown by Figure 3. In this form the magnet is not illustrated. The rotor 71 carries a compensator differing in shape from that shown in Figure 3. This form of compensator comprises an apertured base 109 from the oppo-" the sameas in the form of invention shown by Figure 3. The greater electrical resistance of the speed cup tending to cause to the readings to be too low at high temperature is compensated by the lesser permeability of the compensator causingan increase in the effective magnetic field.

I claim: I i 1. In combination, a bar 1 base portion and ends extending angularly from said base portion, said ends of said magnet being curved in transverse cross-section,

magnet having a and a thermo-sensitive compensator within said magnet, said compensator being secured to said base portion of said magnet and having slotted wings contactingwith the corners at said ends of said magnet.

2. In combination, a bar magnet having a ase portion and ends bent back toward each other and at an acute angle tosaid base por tion, and a thermo-sensitive compensator 

